The present invention relates to an improved electrostatic copying apparatus, of the image transfer type, in which an image, such as a toner image, formed on the surface of an image bearing member is transferred to the surface of a transfer medium such as copy paper advanced in engagement with the image bearing surface.
In copying apparatus of the subject type, transfer paper is transported from a copy paper feed station to a transfer station upon the start of a copying operation. During such transport, paper particles and similar dust particles are produced by the frictional contact of the surface of the copy paper with the periphery of a feed roller at the feeding station and also by the frictional contact of the surfaces of the paper with the peripheries of transport rollers provided in the path of transport of the paper or with the surfaces of transport guide plates. Further, with copying apparatus in which an elongated web of the copy paper wound in a roll is successively cut into individual sheets of copy or transfer paper, the paper web, when cut, releases a large amount of paper particles. Much of the dust thus produced adheres chiefly to the surfaces and forward edge of the transported transfer paper. In the apparatus of the type described, therefore, the transfer paper having such dust deposited thereon is fed to the transfer station, and is the source of numerous objections.
Among the objections which may be encountered with a toner image transfer type electrophotographic copying apparatus which is presently in wide use wherein a latent electrostatic image is formed on the surface of an electrophotographic photoconductive member serving as the image bearing member and which is then developed to a toner image, is that when the toner image on the surface of the photoconductive member is electrostatically transferred to the transfer paper advanced into engagement with the photoconductive member, much of the dust on the transfer paper is attracted to the photoconductive surface. Consequently, the following drawbacks may result from the thus attracted dust.
The copying apparatus of the above image transfer type includes a cleaning unit by which the residual or excess toner remaining on the surface of the photoconductive member is removed therefrom after the transfer of the toner image to the copy paper. When the cleaning unit is a so-called blade cleaning unit equipped with a blade member which has a forward edge in pressing contact with the photoconductive surface, dust particles tend to agglomerate at the forward edge portion of the blade member to raise the forward edge of the blade member by the agglomerated dust particles, possibly holding the blade member locally out of proper pressing contact with the photoconductive surface. This seriously impairs the residual toner removing function of the blade cleaning unit.
Moreover, with the above described type of copying apparatus provided with a device by which the residual toner removed from the surface of the photoconductive member is recovered and then returned to the developing unit for reuse in developing latent electrostatic images, dust particles may mingle with the developer in the developing unit, thereby degrading the developer especially in its transportability and exerting an adverse effect on the development of the latent images. The dust also produces blank dots or the like on the copy image.
Accordingly, it is highly desirable to eliminate the above problems and their consequent drawbacks, especially with the toner image transfer type electrophotographic copying apparatus.